1. Field of the Invention
This specification relates to a molded case circuit breaker, and more particularly, a molded case circuit breaker, capable of preventing an occurrence of a fault by allowing for recognizing a state of the molded case circuit breaker from the exterior without an error, in a manner of preventing a handle from being moved to an OFF position when a fixed contactor and a movable contactor are fused to each other.
2. Background of the Invention
In general, a molded case circuit breaker (MCCB) is installed in a switchboard among electric power receiving and distribution facilities of factories, buildings and the like, so as to serve as a switching device of supplying power or cutting off power to a load side in a non-load state, and serve as a circuit breaker of supplying power or cutting off power from a power source side to the load side to protect an electric line of an electric circuit and a device of the load when a high current exceeding a load current flows due to an occurrence of a fault on an electric circuit of the load during the use of the load.
FIG. 1 is a schematic sectional view illustrating a configuration of the related art molded case circuit breaker, FIG. 2 is a schematic sectional view illustrating a state when the related art molded case circuit breaker is located at an ON position, and FIG. 3 is a schematic view illustrating a state where a lever is rotated to an OFF position while the related art molded case circuit breaker is in a fused state.
As illustrated in FIGS. 1 to 3, the related art molded case circuit breaker is connected to an upper electric line through a fixed contactor 60, and perform switching of inner lines thereof through a movable contactor 50.
The movable contactor 50 may be locked (restricted) by a shaft 40 and a contact spring 80. The movable contactor 50 comes in contact with or is separated from the fixed contactor 60 while performing a rotational motion centering on the shaft 40.
Also, a position of a lever 10 connected with a handle is decided by rotating the handle in response to a user's manipulation. Directions of weight and force change according to the position of the lever 10. Accordingly, strength of force applied through a main spring 70 connected to the lever 10 may differ.
Here, force generated by an elastic force of the main spring 70 is transferred to the shaft 40 through a lower link 30 such that the shaft 40 can perform a rotational motion. Also, the movable contactor 50 rotatably connected to the shaft 40 also cooperatively rotates, thereby switching on or off the molded case circuit breaker. Here, the lower link 30 is rotatably connected to the shaft 40 by use of a shaft pin 41. In this instance, contact pressure is decided by a contact spring 80.
As illustrated in FIG. 2, an angle between a lower end point 70a of the main spring 70 and a rotation point 10a of the lever 10 is designed to be about 5° when the molded case circuit breaker is located at an ON position. Under a condition that the movable contactor 50 and the fixed contactor 60 are in a bonded state due to fusion occurred between the movable contactor 50 and the fixed contactor 60, even though the lower end point 70a of the main spring 70 is moved toward the rotation point 10a of the lever 10 in response to a counterclockwise rotation of a lower end of the lower link 30 by an extra contact angle of the shaft 40, as illustrated in FIG. 3, it is designed that a rotation point of the main spring 70 is located ahead of the rotation point 10a of the lever 10.
Therefore, in a state where the lever 10 has been rotated from an ON state into an OFF state due to a weight by the main spring 70 generated only at the front of the rotation point 10a of the lever 10, when a manipulation force is removed, the lever 10 is returned to an ON position by the main spring 70 and the molded case circuit breaker displays an ON state. This function is referred to as a main contact location function.
The main contact location function will be described in more detail. For a current-limiting circuit breaker, when a fault current is generated on a load or an electric line, the least operation time called an unlatch time is taken to release a mechanical mechanism.
Upon generation of a fault current, during a shorter time than the least operation time, the movable contactor 50 and the fixed contactor 60 are separated from each other due to an electronic repulsive force between contacts, and accordingly a space is generated between the movable contactor 50 and the fixed contactor 60. In this instance, heat of high temperature is generated in the space due to increased resistance, thereby fusing the contacts.
In this instance, the contacts are kept closed without being open due to the fusion. Here, a function that the handle is restored to an ON position without being located at an OFF position refers to the main contact function.
For a molded case circuit breaker, the main contact location function can be made up for in a manner that the lower end point 70a of the main spring 70 is set to be located more forward (ahead) upon designing a product. However, when the molded case circuit breaker is located at the ON position, there is a limit on an angle between a weight axis of the main spring 70 and the lower link 30, which does not allow the lower end point to be located more forward.
The related art molded case circuit breaker performs its original function under an ideal condition. However, actually-produced products frequently faces a case of failing to perform the original function due to friction between components and a movement, which is caused by accumulated assembly tolerance among products.
Also, an angle between the rotation point 10a of the lever 10 and the lower end point 70a of the main spring 70 serves as an important factor of deciding a position of the lever 10. When the angle between both of the points is reduced, a restoring force of the lever 10 toward the ON position by virtue of the main spring 70 is lowered.
Therefore, when a small angle is formed between both of the points for the related art molded case circuit breaker, a problem that the lever 10 fails to return to the ON position has been caused. In addition, as the rotation point of the main spring 70 is located more backward than the rotation point of the lever 10 due to the movement caused by the accumulated assembly tolerance, the lever 10 is moved to the OFF position without returning to the ON position, and the molded case circuit breaker externally outputs an OFF state. Accordingly, the movable contactor 50 and the fixed contactor 60 which are in a contact state due to being fused to each other but they are externally recognized as being in the OFF state in which they are separated from each other. This may bring about an electric shock accident to an operator who has recognized that the molded case circuit breaker is in the OFF state.